Light emitting diode and method for manufacturing the same

ABSTRACT

A light emitting device includes a substrate having a top surface and an bottom surface and a light emitting structure on the substrate, disposed closer to the substrate top surface than the substrate bottom surface, having an n-type conductive type semiconductor layer, a p-type conductive type semiconductor layer, and an active layer. The light emitting device also includes a transparent electrode layer, a first electrode, and a second electrode. The substrate has side surfaces extending from the substrate bottom surface to the substrate top surface, the side surfaces inclined outwardly as the substrate extends in a direction from the substrate bottom surface to the substrate top surface. The transparent electrode layer overlaps more than 50% of a total area of the substrate bottom surface, and a part of light generated by the light emitting structure is emitted to outside via the transparent electrode layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of co-pending U.S. application Ser.No. 13/308,146 filed on Nov. 30, 2011, which is a continuation of U.S.application Ser. No. 12/438,808 filed on Feb. 25, 2009, now U.S. Pat.No. 8,404,566, issued Mar. 26, 2013, which is the national phase of PCTinternational Application No. PCT/KR2007/004587 filed on Sep. 20, 2007,and which claims priority to Korean Patent Application No.10-2006-0092732 filed on Sep. 25, 2006. The entire contents of all ofthe above applications are hereby incorporated by reference.

DESCRIPTION

1. Technical Field

Embodiments relate to a light emitting diode and a method formanufacturing the same.

2. Background Art

Light emitting diodes (LEDs) are manufactured through a scribing processof separating a plurality of unit chips after forming a compoundsemiconductor on the substrate.

The scribing process is to irradiate laser onto a substrate or acompound semiconductor. The substrate or the compound semiconductor,which is adjacent to a scribing region irradiated with the laser, may bedamaged during the laser irradiation.

A portion of light generated from an active layer of the LED is emittedto the outside through the scribing region. However, it is difficult forlight to pass through a portion of the substrate or the compoundsemiconductor damaged by the laser, which degrades light efficiency ofthe LED after all.

DISCLOSURE Technical Problem

Embodiments provide a light emitting diode (LED) and a method formanufacturing the same.

Embodiments provide an LED with improved light efficiency and a methodfor manufacturing the same.

Technical Solution

An embodiment provides a method for manufacturing a light emitting diode(LED), comprising: forming a semiconductor layer; forming a mask layeron the semiconductor layer; irradiating laser onto a scribing region ofthe mask layer to divide the semiconductor layer into a plurality oflight emitting diodes; etching the scribing region; removing the masklayer; and separating the plurality of light emitting diodes.

An embodiment provides a method for manufacturing a light emittingdiode, comprising: forming a semiconductor layer on a substrate; forminga mask layer on the semiconductor layer; irradiating laser onto ascribing region of the substrate to divide the substrate into aplurality of light emitting diodes; etching the scribing region;removing the mask layer; and separating the plurality of light emittingdiodes.

An embodiment provides a light emitting diode comprising: a substrate; asemiconductor layer on the substrate; and an electrode on thesemiconductor layer, wherein the substrate or the semiconductor layerhas at least one etched side surface having a predetermined tilt angle.

The details of one or more embodiments are set forth in the accompanyingdrawings and the description below. Other features will be apparent fromthe description and drawings, and from the claims.

Advantageous Effects

Embodiments can provide a light emitting diode (LED) and a method formanufacturing the same.

Embodiments can provide an LED with improved light efficiency and amethod for manufacturing the same.

DESCRIPTION OF DRAWINGS

FIGS. 1 to 6 are sectional views illustrating a light emitting diode(LED) and a method for manufacturing the same according to a firstembodiment.

FIGS. 7 to 11 are sectional views illustrating an LED and a method formanufacturing the same according to a second embodiment.

MODE FOR INVENTION

Reference will now be made in detail to a light emitting diode (LED) anda method for manufacturing the same, examples of which are illustratedin the accompanying drawings.

FIGS. 1 to 6 are sectional views illustrating an LED and a method formanufacturing the same according to a first embodiment.

Referring to FIG. 1, a semiconductor layer 20, a first electrode 31 anda second electrode 41 are formed on a substrate 10 so as to form an LED.

The substrate 10 may include, for example, a sapphire substrate. Thesemiconductor layer 20 has a multi-stacked structure of a compoundsemiconductor, which will be more fully described in FIG. 6 later.

A portion of the semiconductor layer 20 may be selectively etched, andthe first electrode 31 is formed on an etched portion of thesemiconductor layer 20. Accordingly, heights of the first and secondelectrodes 31 and 41 differ from each other even though they are formedon the same semiconductor layer 20.

The embodiment of FIGS. 1 to 6 illustrates sectional views forconvenience in description, which illustrate processes of forming first,second and third LEDs 51, 52 and 53.

Referring to FIG. 2, a mask layer 60 is formed on the semiconductorlayer 20, the first electrode 31 and the second electrode 41.

The mask layer 60 protects the semiconductor layer 20 during a scribingprocess, and is formed of a material which can be wet-etched ordry-etched. A material for used in the mask layer 60 will be describedin detail later.

In FIG. 2, reference numeral 61 denotes a scribing region. In thisembodiment, laser is irradiated onto the scribing region 61 using alaser irradiation apparatus, thus dividing the semiconductor layer 20into the first, second and third LEDs 51, 52 and 53.

Referring to FIG. 3, when the laser is irradiated onto the scribingregion 61, the mask layer 60, the semiconductor layer 20 and thesubstrate 10 in the scribing region 61 are removed.

During laser irradiation, the layers in the scribing region 61 ontowhich the laser is irradiated are damaged, causing a damaged region 12with a rugged surface to be formed, as illustrated in FIG. 3.

The light emitted from the active layer of the LED does not pass throughbut is absorbed at the damaged region 12, and thus the damaged region 12is removed so as to improve light efficiency of the LED in thisembodiment.

The removal of the damaged region 12 may be performed using wet etchingor dry etching process.

The wet etching process is performed using a first etchant including atleast one of hydrochloric acid (HCl), nitric acid (HNO₃), potassiumhydroxide (KOH), sodium hydroxide (NaOH), sulfuric acid (H₂SO₄),phosphoric acid (H₃PO₄) and aluetch (4 H₃PO₄+4 CH₃COOH+HNO₃). Atemperature of the first etchant is between 200° C. and 400° C.

The mask layer 60 prevents the semiconductor layer 20 from being etchedduring the etching of the damaged region 12. The mask layer 60 may beformed of, for example, silicon nitride (Si₃N₄) or an oxide-basedmaterial such as silicon oxide (SiO₂), which is hardly etched by thefirst etchant.

That is, the first etchant has a higher etch selectivity to the damagedregion 12 than to the mask layer 60.

Since the mask layer 60 is hardly etched by the first etchant, thedamaged region 12 can be selectively etched while minimizing the etchamount of the semiconductor layer 20.

The dry etching may be performed through an inductively coupled plasma/reactive ions etcher (ICP/RIE) or an RIE. In addition, the dry etchingmay be performed using a first etching gas including at least one ofBCl₃, Cl₂, HBr and Ar.

The mask layer 60 configured to prevent the semiconductor layer 20 frombeing etched during the etching of the damaged region 12 may be formedof an oxide-based material such as SiO₂, TiO₂ and ITO or a metallicmaterial such as Cr, Ti, Al, Au, Ni and Pt, which is hardly etched bythe first etching gas.

That is, the first etching gas has a higher etch selectivity to thedamaged region 12 than to the mask layer 60.

The wet etching and the dry etching may be performed for several minutesto several tens of minutes depending on etching environments. FIG. 4illustrates that the damaged region 12 of the scribing region 61 isremoved.

Referring to FIG. 5, the mask layer 60 formed on the semiconductor layer20 is removed after the removal of the damaged region 12.

The removal of the mask layer 60 may be performed using at least one ofthe wet etching and the dry etching.

For example, the mask layer 60 is removed through the wet etching usinga second etchant including at least one of buffer oxide etchant (BOE) orhydrofluoric acid (HF).

Because the semiconductor layer 20 is hardly etched by the secondetchant, the mask layer 60 can be selectively etched while minimizingthe etch amount of the semiconductor layer 20.

That is, the second etchant has a higher etch selectivity to the masklayer 60 than to the semiconductor layer 20.

For example, the mask layer 60 is removed through the dry etching usinga second etching gas including at least one of O₂ and CF₄.

The mask layer 60 can be selectively etched while minimizing the etchamount of the semiconductor layer 20 because the semiconductor layer 20is hardly etched by the second etching gas.

That is, the second etching gas has a higher etch selectivity to themask layer 60 than to the semiconductor layer 20.

Thereafter, a physical impact is applied to the substrate 10 and thesemiconductor layer 20, so that the first LED 51, the second LED 52 andthe third LED 53 are separated from each other by the scribing region61.

A lapping process may be performed to reduce the thickness of thesubstrate 10 before applying the physical impact to the substrate 10 andthe semiconductor layer 20. The lapping process may be performed throughat least one process of chemical mechanical polishing (CMP), dryetching, wet etching and mechanical polishing using slurry.

FIG. 6 illustrates the first LED 51 separated by the scribing region.

The first LED 51 includes the semiconductor layer 20, the firstelectrode 31 and the second electrode 41 which are formed over thesubstrate 10.

The semiconductor layer 20 includes a buffer layer 21, an n-typesemiconductor layer 22, an active layer 23, a p-type semiconductor layer24 and a transparent electrode layer 25.

The buffer layer 21 relieves stress between the substrate 10 and then-type semiconductor layer 22 and enables the semiconductor layer toeasily grow. The buffer layer 21 may have at least one structure ofAlInN/GaN, In_(x)Ga_(1−x)N/GaN andAl_(x)In_(y)Ga_(1−x−y)N/In_(x)Ga_(1−x)N/GaN.

The n-type semiconductor layer 22 may include a GaN layer doped withsilicon, and may be formed by supplying silane gas containing n-typedopant such as NH₃, trimethylgallium (TMGa) and Si.

The active layer 23 may have a single-quantum well or a multi-quantumwell (MQW) structure formed of InGaN/GaN. The p-type semiconductor layer24 may be formed of trimethylaluminum (TMAl),bis(ethylcyclopentadienyl)magnesium (EtCp2Mg), or ammonia (NH₃).

The transparent electrode layer 25 is formed of a material such as ITO,ZnO, RuOx, TiOx and IrOx. The first electrode 31 may be formed oftitanium (Ti) and the second electrode 41 may be formed of a metallicmaterial such as nickel (Ni).

The first LED 51 emits light from the active layer 23 when a power issupplied to the first and second electrodes 31 and 41.

In FIG. 6, a point light source 70 is exemplarily illustrated. A portionof the light emitted from the point light source 70 is reflected by thesubstrate 10 and emitted to the outside through sides of the first LED51.

Since the damaged region 12 on the sides of the first LED 51 has beenremoved through the wet etching or the dry etching, the light isscarcely absorbed at the sides of the first LED 51, and thus it ispossible to effectively emit the light to the outside.

FIGS. 7 to 11 are sectional views illustrating an LED and a method formanufacturing the same according to a second embodiment.

Referring to FIG. 7, a semiconductor layer 20, a first electrode 31 anda second electrode 41 are formed on a substrate 10 so as to form an LED.In addition, a mask layer 60 and a support member 80 are formed on thesemiconductor layer and the first and second electrodes 31 and 41.

The substrate 10 may include, for example, a sapphire substrate. Thesemiconductor layer 20 has a multi-stacked structure of a compoundsemiconductor.

A portion of the semiconductor layer 20 may be selectively etched, andthe first electrode 31 is formed on the etched portion of semiconductorlayer 20. Accordingly, heights of the first and second electrodes 31 and41 differ from each other even though they are formed on the samesemiconductor layer 20.

The embodiment of FIGS. 7 to 11 illustrates sectional views forconvenience in description, which illustrate processes of forming first,second and third LEDs 51, 52 and 53.

The mask layer 60 protects the semiconductor layer 20 during a scribingprocess, and is formed of a material which can be wet-etched ordry-etched.

The support member 80 prevents damages of the first, second and thirdLEDs 51, 52 and 53 which may be caused by a physical force applied tothe first, second and third LEDs 51, 52 and 53 while laser is irradiatedonto the substrate 10 using a laser irradiation apparatus and then thedamaged region of the substrate 10 due to the laser irradiation isremoved by wet or dry etching.

Further, the support member 80 prevents the separation of the first,second and third LEDs 51, 52 and 53 caused by external impact before aprocess of separating the first, second and third LEDs 51, 52 and 53 iscompleted.

The support member 80 may be formed of at least one of an adhesive tape,a material which can be wet-etched or dry-etched, a metallic materialand a wafer substrate.

The support member 80 may be selectively formed depending on thicknessesof the substrate 10 and the semiconductor layer 20. Thus, the supportmember 80 may be omitted.

In FIG. 7, reference numeral 11 denotes a scribing region. In secondembodiment, laser is irradiated onto the scribing region 11 using alaser irradiation apparatus, thus dividing the substrate 10 into thefirst, second and third LEDs 51, 52 and 53.

A lapping process may be performed to reduce the thickness of thesubstrate 10 before irradiating the laser onto the scribing region 11.The lapping process may be performed through at least one process ofchemical mechanical polishing (CMP), dry etching, wet etching andmechanical polishing using slurry.

Referring to FIG. 8, when the laser is irradiated onto the scribingregion 11, the substrate 10 of the scribing region 11 is selectivelyremoved.

During laser irradiation, the layers in the scribing region 11 ontowhich the laser is irradiated are damaged, causing a damaged region 12with a rugged surface to be formed, as illustrated in FIG. 8.

The light emitted from the active layer of the LED does not pass throughbut is absorbed at the damaged region 12, and thus the damaged region 12is removed so as to improve light efficiency of the LED in thisembodiment.

The removal of the damaged region 12 may be performed using a wetetching or dry etching process.

The wet etching process may be performed using a first etchant includingat least one of hydrochloric acid (HCl), nitric acid (HNO₃), potassiumhydroxide (KOH), sodium hydroxide (NaOH), sulfuric acid (H₂SO₄),phosphoric acid (H₃PO₄) and aluetch (4 H₃PO₄+4 CH₃COOH+HNO₃). Atemperature of the first etchant is between 200° C. and 400° C.

The mask layer 60 prevents the semiconductor layer 20 from being etchedduring the etching of the damaged region 12. The mask layer 60 may beformed of, for example, silicon nitride (Si₃N₄) or an oxide-basedmaterial such as silicon oxide (SiO₂), which is hardly etched by thefirst etchant.

Since the mask layer 60 is hardly etched by the first etchant, thedamaged region 12 can be selectively etched while minimizing the etchamount of the semiconductor layer 20.

The dry etching may be performed using an ICP/RIE or an RIE. Inaddition, the dry etching may be performed using a first etching gasincluding at least one of BCl₃, Cl₂, HBr and Ar.

The mask layer 60 configured to prevent the semiconductor layer 20 frombeing etched during the etching of the damaged region 12 may be formedof an oxide-based material such as SiO₂, TiO₂ and ITO or a metallicmaterial such as Cr, Ti, Al, Au, Ni and Pt, which is hardly etched bythe first etching gas.

The wet etching and the dry etching may be performed for several minutesto several tens of minutes depending on etching environments. FIG. 9illustrates that the damaged region 12 of the scribing region 11 isremoved.

Referring to FIG. 9, the mask layer 60 and the support member 80 formedon the semiconductor layer 20 are removed after the removal of thedamaged region 12.

The support member 80 may be differently removed depending on kinds ofthe support member 80. For example, the support member 80 formed ofadhesive tape is removed by detaching it, whereas the support member 80formed of an etchable material is removed by etching process.

The removal of the mask layer 60 may be performed using at least onemethod of the wet etching and the dry etching.

For example, the mask layer 60 is removed through the wet etchingprocess using a second etchant including at least one of buffer oxideetchant (BOE) or hydrofluoric acid (HF).

Because the semiconductor layer 20 is hardly etched by the secondetchant, the mask layer 60 can be selectively etched while minimizingthe etch amount of the semiconductor layer 20.

For example, the mask layer 60 is removed by the dry etching using asecond etching gas including at least one of O₂ and CF₄.

The mask layer 60 can be selectively etched while minimizing the etchamount of the semiconductor layer 20 because the semiconductor layer 20is hardly etched by the second etching gas.

Thereafter, a physical impact is applied to the substrate 10 and thesemiconductor layer 20, and thus the first LED 51, the second LED 52 andthe third LED 53 are separated from each other by the scribing region11.

FIG. 11 illustrates the first LED 51 separated by the scribing region11.

The first LED 51 includes the semiconductor layer 20, the firstelectrode 31 and the second electrode 41 which are formed over thesubstrate 10.

The semiconductor layer 20 includes a buffer layer 21, an n-typesemiconductor layer 22, an active layer 23, a p-type semiconductor layer24 and a transparent electrode layer 25.

The buffer layer 21 relieves stress between the substrate 10 and then-type semiconductor layer 22 and enables the semiconductor layer toeasily grow. The buffer layer 21 may have at least one structure ofAlInN/GaN, In_(x)Ga_(1−x)N/GaN andAl_(x)In_(y)Ga_(1−x−y)N/In_(x)Ga_(1−x)N/GaN.

The n-type semiconductor layer 22 may include a GaN layer doped withsilicon, and may be formed by supplying silane gas containing n-typedopant such as NH₃, TMGa and Si.

The active layer 23 may have a single-quantum well or a multi-quantumwell (MQW) structure formed of InGaN/GaN. The p-type semiconductor layer24 may be formed of trimethylaluminum (TMAL),bis(ethylcyclopentadienyl)magnesium (EtCp2Mg), or ammonia (NH₃).

The transparent electrode layer is formed of a material such as ITO,ZnO, RuOx, TiOx and IrOx. The first electrode 31 may be formed oftitanium (Ti) and the second electrode 41 may be formed of a metallicmaterial such as nickel (Ni).

The first LED 51 emits light from the active layer 23 when a power issupplied to the first and second electrodes 31 and 41.

In FIG. 11, a point light source 70 is exemplarily illustrated. Aportion of the light emitted from the point light source 70 is reflectedby the substrate 10 and emitted to the outside through sides of thefirst LED 51.

In the LED and the method for manufacturing the same according to theembodiments, the LED having a PN junction is described, which includesthe n-type semiconductor layer, the active layer and the p-typesemiconductor layer. However, a chip separation process according to theembodiments is also available for an LED having a NPN junction where ann-type semiconductor layer, an active layer, a p-type semiconductorlayer and an n-type semiconductor layer are stacked in sequence.

Further, in the LED and the method for manufacturing the same accordingto the embodiments, the chip separation process of an LED having ahorizontal configuration is described, in which the first electrode isformed on the n-type semiconductor layer and the second electrode isformed on the p-type semiconductor layer after the p-type semiconductorlayer, the active layer and the n-type semiconductor layer are partiallyremoved.

However, the chip separation process is also available for an LED havinga vertical configuration in which the substrate including a conductivesubstrate, the first electrode, the n-type semiconductor layer, theactive layer, the p-type semiconductor layer and the second electrodeare sequentially formed. That is, the first electrode is formed betweenthe semiconductor layer and the substrate and the second electrode isformed on the semiconductor layer, respectively.

Any reference in this specification to “a first embodiment,” “anembodiment,” “example embodiment,” etc., means that a particularfeature, structure, or characteristic described in connection with theembodiment is included in at least one embodiment of the invention. Theappearances of such phrases in various places in the specification arenot necessarily all referring to the same embodiment. Further, when aparticular feature, structure, or characteristic is described inconnection with any embodiment, it is submitted that it is within thepurview of one skilled in the art to effect such feature, structure, orcharacteristic in connection with other ones of the embodiments.

Also, it will be understood that when an element is referred to as being‘on’ or ‘under’ another element, it can be directly on/under theelement, and one or more intervening elements may also be present.

INDUSTRIAL APPLICABILITY

A light emitting diode (LED) and a method for manufacturing the sameaccording to the embodiments can be applied to a separation process ofLEDs having a variety of structures.

1. A light emitting device comprising: a substrate comprising a topsurface and an bottom surface; a light emitting structure on thesubstrate, disposing closer to the substrate top surface than thesubstrate bottom surface, and comprising an n-type conductive typesemiconductor layer, a p-type conductive type semiconductor layer on then-type conductive type semiconductor layer, and an active layer betweenthe n-type and p-type conductive type semiconductor layers; atransparent electrode layer on the p-type conductive type semiconductorlayer; a first electrode disposed on the n-type conductive typesemiconductor layer; and a second electrode disposed on and contactingto the transparent electrode layer, wherein the substrate has sidesurfaces extending from the substrate bottom surface to the substratetop surface, the side surfaces inclined outwardly as the substrateextends in a direction from the substrate bottom surface to thesubstrate top surface, wherein the transparent electrode layer overlapsmore than 50% of a total area of the substrate bottom surface, andwherein a part of light generated by the light emitting structure isemitted to outside via the transparent electrode layer.
 2. The lightemitting device in claim 1, wherein a width of the substrate top surfaceis greater than a width of the substrate bottom surface, and wherein aportion of the substrate top surface extends beyond the substrate bottomsurface.
 3. (canceled)
 4. The light emitting device in claim 1, whereinthe active layer comprises at least one of single-quantum well and amulti-quantum well structure comprising of InGaN/GaN.
 5. The lightemitting device in claim 1, wherein the n-type conductive typesemiconductor layer comprises a GaN layer.
 6. (canceled)
 7. The lightemitting device in claim 1, the transparent electrode layer comprises atleast one of ITO, ZnO, RuOx, TiOx, or IrOx.
 8. The light emitting devicein claim 1, wherein the first electrode comprises titanium (Ti).
 9. Thelight emitting device in claim 1, wherein the second electrode comprisesmetallic material.
 10. The light emitting device in claim 1, wherein thesecond electrode comprises nickel (Ni).
 11. The light emitting device inclaim 1, wherein the side surfaces include a tilt angle and a step parthaving an angle different from the tilt angle.
 12. The light emittingdevice in claim 11, wherein a length from the step part to the topsurface is less than a length from the step part to the bottom surfaceof the substrate.
 13. The light emitting device in claim 1, wherein thesubstrate includes a break portion between the top surface and thebottom surface of the substrate.
 14. The light emitting device in claim1, wherein a length of the p-type conductive type semiconductor layer isless than a length of the bottom surface of the substrate.
 15. A lightemitting device, comprising: a substrate; a semiconductor layer on thesubstrate, the semiconductor layer comprising a first semiconductorlayer, an active layer on the first semiconductor layer, and a secondsemiconductor layer on the active layer; a transparent electrode layeron the second semiconductor layer; a first electrode disposed on thefirst semiconductor layer; and a second electrode disposed on andcontacting to the transparent electrode layer, wherein the substrate hasat least one side surface having a predetermined tilt angle, wherein thepredetermined tilt angle is an obtuse angle with respect to a bottomsurface of the substrate, wherein the side surface has an inclined partwith the predetermined tilt angle and a step part outwardly protrudedfrom a top portion of the inclined part, and wherein the step partextends outwardly as the substrate extends in a direction from thebottom surface of the substrate to a top surface of the substrate. 16.The light emitting device in claim 15, wherein the active layercomprises at least one of single-quantum well and a multi-quantum wellstructure comprising of InGaN/GaN.
 17. The light emitting device inclaim 15, wherein the first electrode comprises titanium (Ti).
 18. Thelight emitting device in claim 15, wherein the first conductive typesemiconductor layer comprises a GaN layer.
 19. The light emitting devicein claim 15, wherein the second electrode comprises nickel (Ni).
 20. Alight emitting device comprising: a growing substrate comprising a topsurface and an bottom surface; a light emitting structure on the growingsubstrate, disposing closer to the top surface than the bottom surface,and comprising an n-type conductive type semiconductor layer, a p-typeconductive type semiconductor layer on the n-type semiconductor layer,and an active layer between the n-type and p-type conductive typesemiconductor layer; a transparent electrode layer on the p-typeconductive type semiconductor layer; a first electrode disposed on then-type conductive type semiconductor layer; and a second electrodedisposed on and contacting to the transparent electrode layer, wherein adiagonal line from one corner to another corner of the top surface ofthe growing substrate is longer than a diagonal line from one corner toanother corner of the bottom surface of the growing substrate, whereinthe growing substrate comprises a first side surface and a second sidesurface, the first side surface and the second side surface havinginclined surface, wherein a part of at least one of the first sidesurface or the second side surface of the substrate has a step part, andwherein the transparent electrode layer overlaps more than 50% of atotal area of the bottom surface of the growing substrate.
 21. The lightemitting device in claim 1, further comprising a buffer layer betweenthe substrate and the n-type conductive type semiconductor layer. 22.The light emitting device in claim 21, wherein the buffer layercomprises at least one stacked structure of AlInN/GaN,In_(x)Ga_(1−x)N/GaN, or Al_(x)In_(y)Ga_(1−x−y)N/In_(x)Ga_(1−x)N/GaN.